The interspecific vocal mimicry of the mockingbird is a striking phenomenon that has received little experimental analysis. It is proposed that the proximate determinants of this phenomenon be investigated along the following lines: (1) hand-rearing mockingbirds from 5-10 days of age using, in certain cases, sound-isolation chambers, and "tutoring" them with a variety of heterospecific and synthesized songs; (2) objectively assessing mimicries by comparing the vocalizations of experimental subjects with their tutoring sounds in terms of both gross and fine acoustical structure by means of a newly developed real-time bioacoustic analyzer that lends itself to the use of various quantitative methods for extracting and measuring relevant dimensions in bird vocalizations; (3) monitoring experimental subjects to examine the course of song development and, particularly, to determine the temporal relationship between model sounds and mimetic vocalizations both in immature and adult subjects. This project is expected to contribute to the understanding of vocal learning in birds.